The necessity of decreasing energy consumption to heat and/or cool buildings has thrust foam insulation and factory-made foam core panels into the vanguard of desirable products. Foamed polymeric materials (commonly referred to as "foamed plastic" or "plastic foams" and hereinafter referred to as "foam plastics") have excellent thermal insulation properties and are exceptionally well-suited for use in mass-produced or factory-made panel systems such as are used for wall and roof/ceiling assemblies and also for on-site applications in buildings, on walls, ceilings, decks, roofs, exteriors of tanks and vessels, coverings over pipes, and the like.
Although excellent from an insulation viewpoint, the fire performance of foam plastics has generated deep concern which is not dispelled by continual scattered incidents which have taken their toll. This toll has been attributable in part to the combustibility of the foam plastics, and in part to the generation of smoke and toxic gases due to fire involvement. Accordingly, all model building codes have been amended to ensure a judicious selection and use of the foam plastics.
Much effort has been directed to the problem of making foam plastic structural panels safe when exposed to fire. Numerous journal articles have elaborated on solutions to the problem, and some patents have issued describing improvements in the field of fire protection of rigid foam plastics, particularly those used in the building industry. Among the more recently issued U.S. Patents are the following U.S. Pat. Nos. 3,320,077; 3,718,532; 3,816,234; and 3,967,033.
In particular, U.S. Pat. No. 3,967,033 to Robert E. Carpenter is stated to be directed to a fire resistant panel designed to meet requirements stipulated in a testing procedure designated ASTM E-119-73. Fire retardancy or "flame spread rating" is defined as: a measurement of the speed of flame travel across a given surface in accordance with a testing procedure designated ASTM E-84 (also referred to as "the 10-minute Steiner Tunnel Test"). Some prior art panels have an acceptable flame spread rating and are deemed fire retardant, but have unacceptable fire protection. Fire protection is numerically quantified by a "fire endurance (fire resistance) rating" defined as: a determination of the time it takes for a given material or assembly of materials to reach a failure point, based on a testing procedure designated ASTM E-119-76 (a controlled, actual fire exposure). Thermal barrier products of this invention are both fire retardant and fire resistant.
It should be noted that several conventional products provide fire retardance and fire resistance. Among them are gypsum plaster, magnesium oxychloride, Portland cement plaster, concrete, mineral fibers and mastics. In addition, there are lightweight aggregates such as perlite, mica, glass fibers, glass beads, and vermiculite inter alia, some of which may be used with a binder. Most of these products have limitations. The ones that are water-based take several hours to cure, and after curing, are porous, with a resultant loss of some properties such as adhesion and protection against water vapor transmission. Thick coatings are heavy and characteristically exhibit inadequate initial and post-cure adhesion to foam substrates. In some cases the coatings crack and spall because durability, hardness and impact properties are inadequate. Many of these prior art products have poor water vapor transmission properties, that is, they lack protection against water vapor, and permit water degradation of the plastic foam substrate.
Commonly, because of the foregoing problems, building codes require that foam plastic insulation be protected by a 1/2 inch (0.5 in) thickness of gypsum wall board or other material which will limit the temperature rise of the foam plastic surface to not more than 325.degree. F. after 15 minutes exposure to the ASTM E-119-76 standard time-temperature curve. However, the thermal barrier must remain in place during the test, and this usually requires the extensive use of fasteners which is not economical. Metal clad panels with foam plastic cores are covered by the requirements of building codes and therefore a thermal barrier interposed between the foam plastic and the metal cladding is also desirable. The thermal barrier of this invention is particularly well suited for such uses.
It is known that aluminum trihydrate in a polyester resin composition functions as a flame retardant. Upon heating, aluminum trihydrate (about 35% by weight water) releases water of crystallization at about 600.degree. F. in the form of steam, lowers the surface temperature, and thus retards flame propagation. Magnesium oxychloride (about 54% by weight water) also releases its water when heated at about 600.degree. F. In economical thermal barrier thicknesses, these temperatures at which aluminum trihydrate and magnesium oxychloride release the water of crystallization is too high to fire protect foam plastics which begin to decompose at much lower temperatures. The precise decomposition temperature of a foam plastic will vary depending upon its chemical and physical properties. The decomposition temperature of polyurethane foams will typically range from about 300.degree. F. to about 350.degree. F.; polyester foams will range from about 275.degree. F. to about 375.degree. F.; and polystyrene foams will range from about 200.degree. F. to about 300.degree. F. All conventionally used plastic foams decompose at temperatures substantially below 600.degree. F. At about 325.degree. F., thermoset polyurethane foams act as thermoplastic foams and begin to lose their physical properties.
To cope with the problem of relatively low decomposition temperatures characteristics of commercial foam plastics, water fillable polymers were evaluated for fire resistance by ablation when exposed to fire. Such water fillable polymers are disclosed in "Water Fillable Polymers - Ablative Material for Fire Resistance" by J. P. Davidson, et al., California University, 1973, published by National Technical Information Service, U.S. Department of Commerce, Springfield, Va. 22151.
A similar thermal barrier which releases water at a relatively low temperature is a solid water-in-oil emulsion wherein the continuous phase is a thermoset polymerization product of an unsaturated linear polyester and a vinyl monomer cross-linking agent disclosed in U.S. Pat. No. 3,967,033; except that the water is not chemically bound and can be lost under end-use conditions. Besides the resultant loss in fire resistance, the water loss will adversely affect the plastic foam substrate and metal skin covering it. Such water extended polyester thermal barrier is not recommended for use over foam when the thermal barrier is left exposed.